1. Field of the Invention
This invention relates generally to a power hand saw with a movably mounted blade guard and, more particularly, to such a power hand saw in which movement of the blade guard is powered.
2. Description of the Related Art Including Information Disclosed Under 37 C.F.R. 1.97-1.99:
Power hand saws of the type having a circular rotary blade driven by an electrical motor or other source of drive power and having a retractable blade guard are well known. The blade guard is mounted for movement between a guarding position and a nonguarding position. When in the guarding position, the blade is located in a protective relationship with respect to a preselected portion of the circular blade. A coil bias spring resiliently holds the blade guard in the guarding position. Generally, when the foot, or table, of the saw is slid along the work piece, the work piece engages the guard to move it against the force of the bias spring toward a nonguarding position to enable cutting engagement of the blade with the work piece. When the saw is disengaged from the work piece, the bias spring returns the guard to the guarding position.
A problem is encountered when attempting to make a cut adjacent an end of the work piece at which the blade guard is not engageable by the work piece to move it to the nonguarding position. In other instances, without retracting the guard, the blade will cut into the work piece, but the relatively thin portion being cut from the end becomes trapped between the blade and the guard and jams or blocks further movement. In the past, this problem has been addressed in a number of different ways.
In some saws, a handle is mounted to the guide to enable manual movement of the guard to the nonguarding position but this is awkward and difficult, particularly if the user is in a position such as the edge of a roof, cutting rafters. Moreover, such handle disadvantageously locates the user's hand dangerously near the blade. Overcoming this disadvantage are a number of power saws in which the guide is moved to a nonguarding position by powered means.
In U.S. Pat. No. 2,722,246 issued Nov. 1, 1955 to Arnoldy for "Safety Guards for Power Saws", a solenoid partially retracts the guard in response to actuation of a blade drive switch also used to energize the blade drive motor. Accordingly, selective nonretraction of the guard during energization of the blade drive motor is not possible.
Likewise, in U.S. Pat. No. 3,613,748 issued Oct. 19, 1969 to DePue for "Safety Guard Arrangement for Circular Saw", a solenoid is actuated each time power is applied to the blade drive motor and thus retracts the guard during each and every operation of the saw.
In U.S. Pat. No. 3,063,481 issued Nov. 13, 1962 to Sutherland for "Power Saw Guard Retractor", a rubber friction drive wheel is manually moved into engagement with the guard to selective cause it to retract when power is applied to the saw blade. Disadvantageously, in addition to being an awkward means of control, this powered drive guard is capable of only raising the guard after the blade is actively being driven. In addition, the drive requires use of a rubber friction drive roller which is subject to slippage and chemical deterioration from oil on the blade as well as to relative rapid mechanical wear.